1. Field of Invention
The present invention relates to fluid T-sensors. More particularly, the present invention relates to fluid T-sensors that are capable of altering a location of a diffusion interface between at least two fluids flowing in a diffusion space within a main conduit relative to a sensing zone of at least one sensor that is fixed relative to the main conduit without altering the fixed location of the at least one sensor relative to the main conduit.
2. Description of Related Art
H-filters were developed in the late 1990's. In their simplest form, H-filters combine two or more fluid flows into a combined, side-by-side, laminar flow stream. Over the length of the filter, species in the fluids diffuse from one flow stream into another. Slow diffusing species tend to remain in the original laminar flow stream over a finite period of time, whereas fast diffusing species tend to appear or “occur” in the other laminar flow stream within the same finite period of time. In an H-filter, the streams are separated at the end of the combined flow stream, which effectively filters out or separates fast-diffusing species from slow-diffusing species without the need for membranes and other components that require cleaning or replacement.
Conceptually, a T-sensor is similar to the first half of an H-filter. Chemical detection of the diffusing species is completed in the combined laminar flow stream. Post-separation can be conducted, but is not required. Thus, a T-sensor can be considered as a simplification of an H-filter, which includes the combining T but does not require the separation T.
FIG. 1 is a schematic illustration of a basic T-sensor 10 that combines two separate input fluids flowing in the direction of arrows 20, 30, respectively, into a laminar flow shown by arrows 40 through a main conduit 50. Diffusion begins immediately after the two input fluids contact each other at a diffusion start point (time=0) 60, and proceeds perpendicular (lateral) to the flow direction over time. The lateral position is the equivalent of diffusion distance, as indicated by arrow 70. As different chemical species diffuse at different rates, they tend to stratify laterally toward the end of the filter/sensor. The longitudinal position within the filter/sensor (along the direction of flow) is equivalent to diffusion time 80 by the scale factor of (approximately) the flow rate (the horizontal dashed line 90 represents the diffusion interface between the two input fluids, and the lateral dashed lines tipped by arrows 100, 110 represent the extent to which species from one input fluid have diffused into the other input fluid). It will be appreciated that the actual equivalence is more complex since the laminar flow rate varies across the flow cross-section. Fast diffusing species spread uniformly while slow diffusing species stay mostly on their original side of the flow. Thus, the fast diffusing species occur or appear on the opposite side isolated from the slow diffusing species. This property of the filter/sensor is especially useful if one of the combined flows is a carrier fluid absent of any relevant species to be separated/detected (e.g., a “zero fluid” such as pure water or solvent, or N2 gas, which could be the input fluid flowing in the direction of arrow 20 in FIG. 1) and another of the combined flows is a mixture of species to be separated/detected (e.g., a “sample”, which could be the input fluid flowing in the direction of arrow 30).
As previously noted, in an H-filter the output of the lateral section of flow furthest into the carrier side of the filter is peeled off, since this portion includes primarily only the fast diffusing species. Other separation techniques can be combined with the diffusion, including electric or magnetic field gradient (polar and polarizable species tend toward the high field). These additional techniques serve to increase the selectivity of the filter/sensor.
Ideally, the number of sensing locations 120 in a T-sensor would be unlimited. An entire sensing image (in the plane of FIG. 1) would capture all times of diffusion after the diffusion start point (along the flow direction) and all distances from the initial diffusion start point on either side of the diffusion interface where the flows are joined at the input T (perpendicular to flow direction). Such an image would contain all the available information on the diffusion, subject to the species selectivity of the sensing method. However, the sensing method often is spatially sparse, for example because of resource limitations. Cavity enhanced absorption spectroscopy (CEAS), such as cavity ring-down spectroscopy (CRDS), is one example of a sensing method that is usually sparse. A separate optical cavity and associated laser beam and optics are usually needed for each spatial location (re-imaging cavities, such as double-confocal, are an exception to this general rule). The resource expense of CEAS makes desirable the effective use of only one or a small number of CEAS cavities. Despite this resource expense and limitation to sparse sampling, CEAS offers extremely high sensitivity allowing for the detection of trace analyte concentrations.
Normally, the entrance apertures of each fluid to be combined in a T-sensor are fixed. Thus, the pressure of the fluid incident on its aperture (relative to the other fluids) and the size of its aperture determine the relative flow from that fluid. A limited number of sensing locations and fixed apertures results in a loss of information compared with the entire image sensing.